Oil-can Delay Method
An alternative echo system was the so-called "oil-can delay" method, which uses electrostatic rather than electromagnetic recording.
Invented by Ray Lubow, the "oil-can" method uses a rotating disc made of anodized aluminium, the surface of which is coated with a suspension of carbon particles. An AC signal is sent to a conductive neoprene "wiper", which transfers the high impedance charge to the disc. As the particles pass by the wiper, they act as thousands of tiny capacitors, holding a small part of the charge. A second wiper reads this representation of the signal, and sends it on to a voltage amplifier, where it is mixed with the original source. To protect the charge held in each capacitor and to lubricate the entire assembly, the disc runs inside a sealed can with enough of a special oil (Union Carbide UCON lb65) to assure an even coating is applied as it spins.
The effect resembles an echo, but the whimsical nature of the storage medium causes variations in the sound that can be heard as a vibrato effect. Some early models featured control circuitry designed to feed the output of the read wiper to the write head, causing a reverberant effect as well.
Many different companies marketed these devices under various names. Fender sold the Dimension IV, the Variable Delay, the Echo-Reverb I, II, and III, and included an oilcan in their Special Effects box. Gibson sold the GA-4RE from 1965-7. Ray Lubow himself sold many different versions under the Tel-Ray/Morley brand, starting out in the early sixties with the Ad-n-echo, and eventually producing the Echo-ver-brato, the Electrostatic Delay Line, and many others into the eighties.
Read more about this topic: Echo Chamber
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